It's a torque-to-yield bolt and a deformable washer.
Replace the bolt and the washer when installing the DMD.

Bolt - F5RZ-6A340-B Bolt, M12x1.5 $3.12
Washer - F1AZ-6378-A Washer, 13.5x39.5 $3.27

Not the place to try and save a buck!

AL


Red '98 SVT E0 3098/6535 DMD other stuff and a Bullitt fuel door